The invention relates to a hydraulically damping rubber bearing engine mount for motor vehicles having two end walls lying opposite one another in the axial direction and two chambers which are designed as pressure and auxiliary chambers and which contain a damping fluid. The two chambers are connected to one another by a restriction orifice and there is an annular rubber-elastic spring element which adjoins the pressure chamber and is secured on one end wall. A diaphragm is fluid-tightly clamped in the pressure chamber and is loaded on one side by the damping fluid and can be loaded on the other side by compressed air which can be fed in from outside. When the diaphragm is loaded by compressed air, an air chamber is formed between the diaphragm and both the spring element and the one end wall, and with the diaphragm being able to lift off from the spring element and the one end wall in response to the compressed air.
A rubber bearing of this general kind is known from DE-OS No. 3,404,593. In the case of this rubber bearing, the cross-section of the restriction orifice between the pressure chamber and the auxiliary chamber is altered stepwise as a function of an external parameter, such as a transmission adjustment. Complete cancellation of the damping effect is not possible in this rubber bearing.
An object on which this invention is based is to develop a rubber bearing of this general type in such a way that the damping effect of the bearing can be altered smoothly and continuously by external intervention right up to complete cancellation, i.e., to the decoupling of the bearing.
The object is achieved according to the invention by having the diaphragm lift off from the spring element and the one end wall either partially, or totally, to provide contact areas of varying sizes over varying regions depending on the amount of air fed and applied to load the diaphragm. When the diaphragm is completely lifted off the spring element and the one end wall, the mount is decoupled.
In the case of the rubber bearing designed according to the invention, an air chamber is built up with the introduction of compressed air into the pressure chamber between the diaphragm and both the rubber-elastic spring element and the end wall adjoining the latter. The diaphragm lifts smoothly and progressively further off from the end wall and the spring element as the air chamber grows bigger. Since the compressible air in the air chamber can transmit virtually no damping force between the damping fluid on the one hand and the one end wall and spring element on the other hand, damping forces are only transmitted to the spring element in the region of the latter where the diaphragm rests on the spring element. Thus, with the diaphragm lifted off completely from the spring element, damping forces are no longer transmitted and the rubber bearing is decoupled. Thus, in the rubber bearing designed according to the invention, the most favorable damping force can be set exactly, right up to and including the cancellation of damping, simply by feeding in compressed air and this setting can be continuously, smoothly and progressively varied.
The quantity of air in the air chamber is made dependent on the vibrational state of the engine, and/or of the region of the vehicle near to the engine, and/or the nature of the surface to be driven on by the motor vehicle to provide adjustment of the damping forces in a simple manner.
A stop body, which is secured on the diaphragm on the side loaded by fluid, limits the maximum possible extension of the diaphragm and serves for the stabilization and controlled movement of the diaphragm.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing.